25th International Meeting on Organic Geochemistry IMOG 2011

P-101
Formation of giant deep-buried old heavy oil reservoirs below
7000m in Tarim Basin,China
Zhu Guangyou, Zhang Shuichang, Su Jin, Gu Lijing, Wang Yu, Zhang Bin
Research Institute of Petroleum Exploration and Development, PetroChina, Beijing, China (corresponding
author:zhuguangyou@petrochina.com.cn)
Giant heavy oil pools were discovered in deep buried
Ordovician carbonate reservoirs (6500~7000m) in
Tabei area of Tarim basin, China. Ground oil density
ranged from 0.92 g/cm 3 to1.05 g/cm 3 (20℃), viscosity
from 20 to 9142 mPa.s, solidifying point from -16℃ to
-30℃, paraffin content from 2 to 14%,sulfur content
from 0.5 to 3.2%, resin and bitumen from 7 to
20%,average initial gas/oil ratio was 50m 3 /m 3 . All
were non-saturated reservoir. The daily oil production
of heavy oil wells ranged from several tens to several
hundreds m 3 , gas production rate was lower and
averaged at several thousands m 3 . Exploitation were
carried out by adding light oil to heavy oil reservoir.
Analysis of biomarkers indicated that deep heavy oil
major originated from middle-upper Ordovician source
rocks in south depression. High concentration of C25norhopane
showed in mass chromatogram m/z=177
and chromatography of crude oil had obvious bulging
baseline both implied oil had been severely
biodegraded.
Fluid inclusions data obtained from Ordovician
carbonate reservoirs showed hydrocarbon charged
during late Permian. Homogenization temperatures of
fluid inclusions from well H601-4 Ordovician sparite
reservoir(6654m) were concentrated in 83~89℃, fit
the thermal history curve(Fig 1) at late Permian.
Tabei area experienced long time deep bury and
subsidence from Triassic and Ordovician paleohydrocarbon
reservoirs were well preserved.
Densification of Ordovician oil was happened during
late Permian, degradation happened after charging.
Tabei heavy oil reservoir was an old hydrocarbon
system which accumulated before 250Ma and
degraded and experienced long time deep burial.
In conclusion, Deep reservoir of Tabei area in Tarim
basin had large distribution of heavy oil resources,
which formed before 250Ma and was a old deep
heavy oil reservoir. The low geothermal gradient and
quick deep burial since 5Ma were both important
conditions for the preservation of deep heavy oil
reservoir.
Fig 1 Burial history curve of well H601-4 and
distribution diagram of homogenization temperatures
of fluid inclusions
Fig 2 Marine hydrocarbon accumulation in the
northern Tarim Basin evolution profile (N-S direction)
Notes: ①before the sedimentation of upper
Ordovician, sedimentary strata was exposed and
formed karst reservoirs; ② before the sedimentation of
Devonian, strata uplifted, Silurian denuded, enhanced
formation of the karst reservoirs; ③late Hercynian(late
Permian),oil originated from middle-upper Ordovician
source rocks charged from north to south along the
Ordovician karst reservoirs, formed hydrocarbon
pools; ④ before the sedimentation of Triassic,
tectonic uplifted and hydrocarbon in Ordovician
reservoirs biodegraded and formed heavy oil; ⑤since
the sedimentation of Mesozoic, Ordovician reservoirs
experienced sustain quick burial and the paleoreservoir
was well preserved
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